This is a common error when debugging JavaScript for the IE 7 and earlier IE browsers. Essentially, it appears that IE 7 is a little more strict on syntax than IE 8 and it's successors.
While this error is not specific to JSON formatted objects, it can occur when they are not syntactically correct. When dealing with JavaScript Object Notation, ensure that you don't have any "trailing commas". For instance, the following will throw an error in IE 7:
var customLayout: {
'test1' : [ '0 1 2 3 4 5 6 7 8 9'],
'test2' : [ 'q w e r t y u i o p'],
}
Whereas, this JSON object is valid (notice that the final element is not suffixed by a comma:
var customLayout: {
'test1' : [ '0 1 2 3 4 5 6 7 8 9'],
'test2' : [ 'q w e r t y u i o p']
}